1. Field of the Invention
The present invention relates to a broadcast system which distributes a digital broadcast signal via an Internet Protocol (IP) network, and its distribution device and terminal device.
2. Description of the Related Art
In digital broadcasting, including terrestrial digital broadcasting, there exist low-signal-strength areas just as with analog broadcasting. As a countermeasure, a system to transmit a broadcast signal not by radio but through a wired line is needed.
In digital broadcasting, whole items of information to be transmitted are digitized and video information, audio information, data information, and program information consisting of the broadcast signal is multiplexed as digital information to be transmitted. Therefore, as for the countermeasure for the low-signal-strength areas of the broadcast signal, it is possible to use the existing digital network, transmit the broadcast signal as a digital signal, and distribute it to viewers in the low-signal-strength areas.
Therefore, a relay device which converts the received broadcast signal into IP packets to distribute it via an IP network as a multicast is proposed (e.g., refer to Jpn. Pat. Appln. KOKAI Publication 2004-23600).
However, in the case of use of a cable digital network, because an information transmission band of a subscriber accommodation part is limited especially, if the broadcast signal is digitized as it is to be transmitted, a problem, such that sufficient quality cannot be obtained and a large number of channels cannot be freely viewed, occurs.